46 PHYSIOLOGICAL CHEMISTRY 



INULIN, (C 6 HioO 5 ) x 



Inulin is a polysaccharide which may be obtained as a white, odor- 

 less, tasteless powder from the tubers of the artichoke, elecampane, or 

 dahlia. It has also been prepared from the roots of chicory, dandelion, 

 and burdock. It is very slightly soluble in cold water and quite easily 

 soluble in hot water. In cold alcohol of 60 per cent or over it is prac- 

 tically insoluble. Inulin gives a negative reaction with iodine solution. 

 The " yellow" color reaction with iodine mentioned in many books is 

 doubtless merely the normal color of the iodine solution. It is very 

 difficult to prepare inulin which does not reduce Fehling's solution 

 slightly. This reducing power may be due to an impurity. Prac- 

 tically all commercial preparations of inulin possess considerable 

 reducing power. 



Inulin is levo-rotatory and upon hydrolysis by acids or by the 

 enzyme inulase it yields the monosaccharide fructose which readily 

 reduces Fehling's solution. The ordinary amylolytic enzymes occur- 

 ring in the animal body do not digest inulin. A small part of the 

 ingested inulin may be hydrolyzed by the acid gastric juice, but Lewis 1 

 has recently shown that "the value of inulin as a significant source of 

 energy in human dietaries must be questioned." 



EXPERIMENTS ON INULIN 



1. Solubility. Try the solubility of inulin powder in hot and cold water and 

 alcohol. If uncertain regarding the solubility in any reagent, filter and neutralize 

 the filtrate if it is alkaline in reaction. Add a drop of concentrated hydrochloric 

 acid to the filtrate and boil it for one minute. Render the solution neutral or 

 slightly alkaline with solid potassium hydroxide and try Fehling's test. What 

 is the significance of a positive Fehling's test in this connection? 



2. Iodine Test. (a) Place 2-3 c.c. of the inulin solution in a test-tube and 

 add a drop of dilute iodine solution. What do you observe ? 



(b) Place a small amount of inulin powder in one of the depressions of a test- 

 tablet and add a drop of dilute iodine solution. Is the effect any different from 

 that observed above? 



3. Molisch's Reaction. Repeat this .test according to directions given under 

 Glucose, 2, page 21. 



4. Fehling's Test. Make this test on the inulin solution according to the 

 instructions given under Glucose, page 26. Is there any reduction? 2 



5. Hydrolysis of Inulin. Place 5 c.c. of inulin solution in a test-tube, add a 

 drop of concentrated hydrochloric acid and boil it for one minute. Now cool 

 the solution, neutralize it with concentrated\KOH and test the reducing action 

 of i c.c. of the solution upon i c.c. of dilu ed (1:4) Fehling's solution. Also 



1 Lewis: Journal American Medical Ass'n., 58, 1176, 1912. 



2 See the discussion of the properties of inulin, above. 



